A quick coupling engageable under pressure generally comprises a first hollow longitudinal body in which a second longitudinally hollow longitudinal body is inserted supported inside the first body in a longitudinally slidable way in contrast to and by action of appropriate elastic means.
The second body has a housing for an opening and closing valve to the flow of a fluid under pressure through the internal cavity of the second body itself.
The construction of the coupling comprising the second hollow body which is moveable with respect to the first hollow body is as known functional to the locking of the coupling in the engaged position. In fact, the first body and the second body have relevant locking means of the known type, adapted to cooperate for locking the coupling in the engaged position. For that purpose the elastic means operate to automatically recall the second body towards the position corresponding to locking the coupling in the engaged position.
One of the main drawbacks to be overcome when a coupling is to be engaged under pressure consists of the fact that the pressure of the fluid acting in closure on the valve, also generates a force that opposes the movement of the second body with respect to the first body and that consequently opposes the locking of the coupling in the engaged position.
Currently, to overcome this drawback a construction of the coupling is used wherein the internal surfaces wet by the fluid under pressure are configured and arranged to balance the thrust forces in the axial direction generated by the fluid under pressure net of the thrust force in the axial direction exerted by the elastic means.